The motor and its electronic system are supplied by one or several batteries. The vehicle wheel drive can be direct to maximize efficiency or equipped with a speed reducer to minimize the motor size. The proposed solution uses a permanent magnet three-phase motor which can reach four times the nominal torque. This motor structure includes an outer rotor which can be fitted into a vehicle wheel. It can be used as motor or generator with energy recuperation in the battery during braking periods or to create electricity to recharge battery, or power other devices by changing the motor. This motor structure is supplied by a PWM (Pulse Width Modulation) current controlled inverter. The operator can impose the machine torque level in motor or generator operation by setting a current reference. The shape of the alternative phase current waveform is rectangular with a width of 120 electrical degrees. This kind of motor supply is the simplest to realize and it reduces the cost of the control system and the number of sensors.
The brushless motor includes a cylindrical outer rotor wherein permanent magnets are mounted on the surface and an internal stator with coils of insulated wire wound around the teeth. There are twenty-two magnet poles on the rotor alternatively magnetized north and south and twenty-four slots on the stator. This combination of slots and poles for a three-phase motor structure allows the realization of a special concentrated winding around the teeth with only one coil per slot. In this case, there are only twelve coils to realize. The winding coefficient and the copper filling factor are higher than in the other known solutions described by Konecny U.S. Pat. No. 4,774,428, Huang and al. U.S. Pat. No. 5,675,196 and Katsuma and al. U.S. Pat. No. 4,719,378 which are using winding with two coils per slot.
This kind of winding with one coil per slot simplifies the assembling of the rotor position sensors (i.e. hall detectors) near the air gap. The hall detector are fixed on the side of several teeth which have no winding and they are using the leakage flux of the permanent magnets to detect the rotor position.
The proposed structure maximizes the energy efficiency and the motor starting torque per unit volume of winding. The advantages of a concentrated winding around the teeth in comparison with a classical distributed winding are described in Konecny U.S. Pat. No. 4,774,428 and Permanent magnet brushless DC motor with soft metal powder for automotive application by J. Cros and P. Viarouge published in the IEEE Industry applications Society in October 1998. The volume of copper is reduced and subsequently the Joule losses are minimized.
The amount of vibrations and the cogging torque ripple are reduced drastically like in the other structure combinations described by Konecny U.S. Pat. No. 4,774,428, Huang and al. U.S. Pat. No. 5,675,196 and Katsuma and al. U.S. Pat. No. 4,719,378. The least common multiple (LCM) of the motor's poles and slots describes how many peaks of cogging torque will be present over a single revolution of the motor. In this case, there are 264 torque pulses per revolution and consequently, the cogging torque amplitude is very low (less than 3% of the rated torque).
The proposed motor structure also minimizes the net radial force like another structure described by Huang and al. U.S. Pat. No. 5,675,196.
Reference is made to British Patent GB 2 289 991 which discloses a winding sequence for a motor having twelve slots and ten poles. It is described in that Patent the use of a structure and a specific winding sequence wherein one winding per slot is provided to obtain independent magnetic flux flow for each phase.
Japanese Patent A-400 4703 relates to an electric bicycle most specifically to a system capable of detecting the direction of rotation of the rotor as well as its speed by the use of an optical sensor whereby to control the amplitude of the current in the motor.
The electronic supply includes a power electronics supply and a current control electronics circuit. Both systems can be inserted inside the motor housing, in the center of the stator yoke. The power electronics system is composed of an inverter with six MOSFETs or multiple MOSFETs which operate like six MOSFETs. The structure diodes of the MOSFETs are used to ensure the current reversibility. At each sequence of conduction defined by the rotor position detector, two transistors are switched on to supply two motor phases. In the classical mode of operation, a modulation signal is applied on the gate of these two transistors. This method simplifies the control realization and only one current sensor can be inserted in the DC bus for the current measurement.
Another solution consists in applying the modulation signal on one transistor only at each sequence of operation: this method is the single switch modulation technique. The other transistor is switched “on” during all the duration of this sequence of conduction. This mode of operation is described in E.M.I. tests on a brushless actuator: Comparison by M. Lajoie-Mazene and J. P. Berry published in European Power Electronics in September 1993, in the case of monitoring operation only, compared to the classical mode of operation where the modulation signal is applied on the gate of the two transistors. It is shown that the single switch modulation provides lower electromagnetic interferences (EMI) and reduces the commutation losses, the conduction losses in low voltage applications, the current ripple and the size of the input filtering capacitor. The proposed electronic system is using the single switch modulation and it can be used for motor as well as generator operation. Consequently, the current regulation is realized without any external current sensor.
Another article of interest is the Synthesis of high performance PM motors with concentrated windings by J. Cros and P. Viarouge published in the IEEE Transactions on Energy Conversion in June 2002. It explains a method for determining a winding for a concentrated winding motor.